1. Field of the Invention
The invention is in the field of iontophoresis. In particular, the invention relates to disabling automatically an iontophoretic drug delivery device when the device supply voltage falls below a certain level, thereby preventing any further delivery of drugs to the patient under a condition that may compromise the proper operation of the device.
2. Description of the Related Art
Iontophoresis is the application of an electrical current to transport ions through intact skin. One particularly advantageous application of iontophoresis is the non-invasive transdermal delivery of ionized drugs or other therapeutic agents into a patient. This is done by applying low levels of current to a patch placed on the patient's skin, which forces the ionized drugs contained in the patch through the patient's skin and into his or her bloodstream.
Passive transdermal patches, such as those used to deliver nitroglycerin for angina pectoris, estradiol for hormone replacement, and nicotine to stop smoking, can only use a limited number of drugs because they work by diffusion. Iontophoresis advantageously expands the range of drugs available for transdermal delivery, including, for example, parenteral drugs (e.g., peptides). Further, because the amount of drug delivered is related to the amount of current applied, the drug delivery rate can be precisely controlled by controlling the current, unlike the passive transdermal patches. This allows for more rapid delivery (onset) and drug reduction (offset) in the patient.
When compared to drug delivery by needle injection, iontophoresis can have less physical and emotional trauma, pain, and possibility of infection. Transdermal drug delivery by iontophoresis also avoids the risks and inconvenience of IV (intravenous) delivery. In addition, when compared to oral ingestion of drugs, drug delivery by iontophoresis bypasses the GI tract, thus reducing side-effects such as drug loss, indigestion and stomach distress, and eliminating the need for swallowing the drug. Iontophoresis also avoids drug loss due to hepatic first pass metabolism by the liver that occurs when drugs are ingested.
Further, transdermal drug delivery by iontophoresis permits continuous delivery of drugs with a short half life and easy termination of drug delivery. Because iontophoresis is more convenient, there is a greater likelihood of patient compliance in taking the drug. Thus, for all of the above reasons, iontophoresis offers an alternative and effective method of drug delivery, and an especially useful method for children, the bedridden and the elderly.
An iontophoretic drug delivery system typically includes a current source, such as a battery and current controller, and a patch. The patch includes an active reservoir and a return reservoir. The active reservoir contains the ionized drug, for example, in a conductive gel. The return reservoir contains a saline gel and collects ions emanating from the patient's skin when the drug is being delivered into the patient's skin.
The patch also has two electrodes, each arranged inside the active and return reservoirs to be in respective contact with the drug and saline. The anode, or positive, electrode and the cathode, or negative, electrode are respectively electrically connected to the anode and cathode of the current source by electrical conductors. Either the anode electrode or the cathode electrode is placed within the drug reservoir, depending on the charge of the ionized drug. This electrode is designated as the active electrode. The other electrode is placed within the return reservoir, and is designated as the return electrode.
The active electrode has the same charge as the ionized drug to be delivered and the return electrode has a charge opposite of the drug to be delivered. For example, if the drug to be delivered to the patient has a positive ionic charge, then the anode will be the active electrode and the cathode will be the return electrode. Alternatively, if the drug to be delivered has a negative ionic charge, then the active electrode will be the cathode and the return electrode will be the anode. When current from the current source is supplied to the active electrode, the drug ions migrate from the drug gel in the reservoir toward and through the skin of a patient. At the same time, oppositely-charged ions flow from the patient's skin into the saline solution of the return reservoir. Charge is transferred into the return electrode and back to the current source, completing the iontophoretic circuit.
The electronic controller between the battery and the electrodes delivers the required current to the patch. The controller may control the output current so that drug delivery is accomplished at a constant or varying rate, or over a short, long or periodic time interval. These controllers generally require relatively complex electrical circuits, sometimes including microprocessors, to meet the above requirements.
Under ordinary operating conditions, the power supply voltage (e.g., the battery voltage) is above the minimum operating voltage of the device circuitry. In this situation, the operation of the device circuitry is predictable. If the battery voltage drops below the minimum operating voltage, however, operation of the device circuitry becomes unpredictable, and the device circuitry may not function properly.
The electronic controller may be programmed to shut off the current control circuit when a low voltage condition is detected. But this approach only works if the supply voltage is high enough for the controller to operate. If the supply voltage drops below this level, the shut off mechanism may not operate properly.
In particular, if the supply voltage drops below a certain level, and the operation of the components is unpredictable, the current control circuit may supply current to the patch, which would cause the drug to be delivered to the patient. In this malfunction condition, the iontophoretic current may even be higher than the current that is supplied when the supply voltage is correct. If this occurs, higher dosage of drugs could be delivered to the patient.